Tontotralman (who points out that he's NOT a carpenter) built this one-person slide on truck camper to fit inside his 6' truck bed with the tailgate shut. There's no cabover, but he still managed to fit a raised sleeping area inside.
It's built on 2x2 framing with OSB panels, and 1-1/2 styrofoam insulation. The interior is oriented sideways, with a sideways 6.5 foot wide bedroom area over a storage compartment, and front entrance area with storage cupboards on the left and kitchen area on the right.
On the outside he has some storage space between the walls and the bed, and a small electrical hookup. I like the split door idea that allows easy access.
Part 2 shows the finished body with corner trim, ceiling vent, water storage, the completed kitchen area (which looks much like a home kitchenette).
Part 3 shows the aerodynamic nose attached as a cabover extension to be used for lightweight storage in the future. He also explains the split door that allows for an exit when the tailgate is up. A highlight of Part 3 is his upgraded version of a "redneck air conditioner" made from a fan and an ice cooler and upgraded with copper coil and water pump.

Want fresh ideas for simpler more economical ways to cook when you're living off the grid? Look into the cheap and powerful homemade backpacking stoves used by inventive campers like this guy. They're made to be easy to assemble from common items in your recycling bin for just a few bucks at most and run off alcohol or free wooden twigs you find lying around. All in all, much quicker and more efficient than setting up a whole campfire just to boil some water!

Never worry about starting a campfire again! You can easily prepare your own quick lighting emergency "char cloth" with just a tuna can, T-shirt, and a your barbecue grill.
Essentially the video describes making a quick and dirty DIY gasification stove -- like the ones many backpacking survivalists use to cook food -- but the focus of this project is simply to get at the valuable leftover charcoal without the (slight) added complexity of designing an efficient camp stove.
But if you already have a gasifying camp stove -- like the SoloStove or another homemade version -- you can now add versions of "char cloth" to your emergency kit. (I love the cotton balls idea!)

Here's a really awesome DIY Slide On Four Wheel Camper Style Pop-Up Truck Camper RV by 'notesfromavagabond.' It's built on an aluminum frame he welded together himself and includes a few innovative features, such as a fold out room and a simple roof-lift mechanism.
(Thinking about building your own truck camper? (You can build them out of wood, too!) If you haven't yet, check out my article on How To Build Your Own DIY Truck Camper RV)